Messages in this thread | | | Date | Tue, 21 Feb 2006 18:35:48 -0800 | From | Ravikiran G Thirumalai <> | Subject | Re: [patch] Cache align futex hash buckets |
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On Tue, Feb 21, 2006 at 06:08:45PM -0800, Andrew Morton wrote: > Nick Piggin <nickpiggin@yahoo.com.au> wrote: > > > > Christoph Lameter wrote: > > > On Tue, 21 Feb 2006, Nick Piggin wrote: > > > > > > > > >>Ravikiran G Thirumalai wrote: > > >> > > >>>Following change places each element of the futex_queues hashtable on a > > >>>different cacheline. Spinlocks of adjacent hash buckets lie on the same > > >>>cacheline otherwise. > > >>> > > >> > > >>It does not make sense to add swaths of unused memory into a hashtable for > > >>this purpose, does it? > > > > > > > > > It does if you essentially have a 4k cacheline (because you are doing NUMA > > > in software with multiple PCs....) and transferring control of that > > > cacheline is comparatively expensive. > > > > > > > Instead of 1MB hash with 256 entries in it covering 256 cachelines, you > > have a 1MB hash with 65536(ish) entries covering 256 cachelines. > > > > Good (if accidental point). Kiran, if you're going to gobble a megabyte, > you might as well use all of it and make the hashtable larger, rather than > just leaving 99% of that memory unused...
Yes, good (intentional :) ) point. I am rerunning my tests with a larger hash slot. (As large as the padding takes away). If we get the same or better results, we can just increase the hash slots.
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